Much effort has been devoted to making an effective snow guard which is user-friendly as well as economical. A record of the results of the effort go back for over a century, and the effectiveness of a wide array of snow guards in harsh winter conditions in particular parts of the world subject to ice storms and heavy snow falls, is annually put to the test. The basic components of a snow guard are (i) a laminar base or "strap", (ii) a snow-restraining component referred to as a "snow-stop" herein, this component providing the surface area which resists forces exerted by an accumulated snow-pack, and (iii) a "leg" or "web" which supports and reinforces the snow-stop. Considering the simplicity of design of a snow guard it would appear that there is no reason why a snow guard should fail, or result in fracturing a slate or tile on which the snow guard rests. Clearly, casting the critical components, namely (ii) and (iii) of the snow guard will provide a rugged snow guard, but at higher cost than forming at least one of those components of sheet metal. Representative of such snow guards with a cast metal snow-stop having a V-shaped brace for greater reinforcement of the restraining member, is one disclosed in U.S. Pat. No. 1,863,561 to Brinker et al. (1929), and such cast snow-stops are presently popular in the up-scale market despite the known economies of sheet metal snow-stops because the received wisdom is that sheet metal snow-stops are less durable.
The economics of using sheet metal benefitted a conical snow-stop of sheet metal disclosed in U.S. Pat. No. 1,732,936 to Hudson (1929). The conical snow-stop relies on the area presented by the internal surface of the cone to provide resistance, but the sheet metal cone is readily deformed in compression vertically, and collapses under the weight of a person who inadvertently steps on the cone while inspecting the roof or carrying out maintenance on it. Reference to the vertical direction herein is relative to the horizontal plane in which the longitudinal base of the snow guard is presumed to lie when not in use, and not relative to the surface of the roof on which the snow guard is deployed. To provide resistance to deformation by a large vertical compressive force, U.S. Design Pat. No. 364,556 to Bowie (1995) discloses a vertical snow-stop braced with a downwardly tapered axial web. However, the triangular side portions of the snow-stop are not adequately braced by the web, and one or both of these side portions will be deformed under occasional abnormally heavy pressure of a snow-pack.
U.S. Pat. Nos. 625,144 and Des. 30,788 to E. W. Clark (1899) provided the basic design concept which has been modified over the ensuing century. This design provided a laminar base supporting an elevated projection (also referred to as a foot, shelf, cornice or hood) which is reinforced by a web (or "leg"). Key modifications were disclosed during the period from 1925 to 1967 in U.S. Pat. No. 1,530,233 to Campbell, U.S. Pat. No. 1,647,345 to Douglas, and U.S. Pat. No. 3,296,750 to Zaleski. Most recently a sheet metal support with a east bronze foot have been used in U.S. Pat. No. 5,343,659 to Zaleski and U.S. Pat. No. 5,371,979 to Kwiatkowski et al.
To overcome the susceptibility to deformation of the snow-stop under pressure, the '979 patent discloses the restraining member (referred to herein as the snow-stop) being preferably formed by casting a metal such as bronze, aluminum or iron, especially bronze or lead-coated bronze. When combined with a cast web, the snow-stop is effective but less economical than sheet metal. In the '979 configuration, the circumference of the shank of the rivet attaching the support to the leg of the restraining member is "worked" by compressive forces against the restraining member, loosening the interference fit between the shank, the leg and the support. When the fit is loosened, the leg is prone to a pivoting action which engages the down-roof end of the leg against the base of the snow guard, resulting in a camming action. The camming action, in turn, tends to fracture a shingle, particularly if the up-roof end of the laminar base is hooked to the up-roof (front or upper) edge of a shingle. The term "shingle" is used herein to refer to a laminar roofing element which may be slate, tile formed from cement or fired clay, or, a weather resistant organic material such as asphalt, optionally reinforced with inorganic fibers or particulate matter. The foot provides a bending moment which tends to bow the laminar base between its up-roof end where it is attached to the roof, and the base's down-roof (rear or lower) end to which the foot and web are attached. When subjected to substantial forces due to snow loading, cyclically, the bowing not only causes metal fatigue but can also break the underlying shingle. Concern about damage due to bowing is evidenced in the '979 patent where it states, "Regarding the great strength of snow stops hereof, . . . with the base fixed to a test stand and force gauge in a manner to prevent bowing in test performance." (col 4, lines 34-39).
With particular regard to a slate roof, each slate is typically secured with two nails. Because of the angulation of the slate lying over another in a contiguous lower row, the lower surface of a nail's head is spaced apart from the roof deck by nearly twice the thickness of the slate. Therefore such nails driven through a slate, with their heads projecting in spaced-apart relation to the roof's deck are more inclined to bend and shear under high snow loading than nails which are flush-driven through the laminar base of a snow guard, into the deck (see FIG. 6). When a snow guard is hooked on to the up-roof edge of a slate, the slate breaks, serving its sacrificial function to avoid damaging the snow guard. This function was economical in the 19th century when slate or tile and the labor to replace them were relatively inexpensive, in comparison to the cost of copper or brass snow guards. To have to replace either a broken shingle or a damaged snow guard is no longer acceptable.
A snow guard made from a foldable sheet metal, which snow guard comprises a laminar strap, a snow-stop and a gusseted brace, has recently been marketed. The snow-stop comprises (a) an upstanding arcuate member in the form of a semi-circular disc with an unflanged periphery, referred to as a "barrier" which restrains the snow-pack, and (b) a barrier-base, integral with the barrier and bent at right angles thereto so as to provide a laminar base which is secured to the upper surface of the strap. In particular, the gusseted brace provides upstanding generally trapezoidal flange portions, referred to as "trapezoidal tabs", which are button-riveted to the down-roof surface of the barrier. This prior art gusseted brace avoids using a web or leg, and avoids using a rivet which, if worn and loosened in the web, would result in a camming action. The barrier is thus reinforced around the periphery of a pyramid-shaped cavity having a triangular base, formed by the gusseted brace.
However, the unflanged periphery of the barrier of this prior art snow guard fails to provide optimum rigidity of the periphery of the barrier as the trapezoidal tabs reinforce only an inner circumferential portion of the barrier's down-roof area. This inner portion is spaced apart from the periphery, leaving the peripheral portion un-reinforced. This peripheral portion of the down-roof surface of the barrier, which portion is not reinforced by the trapezoidal tabs, is therefore less resistant to down-roof force than the remaining inner portion which is reinforced with the trapezoidal flange portions. In the novel snow guard, the arcuate flange portions, each shaped as a segment, or portion of a segment of a circular disc, leave substantially no peripheral portion of the down-roof surface of the barrier unreinforced.
Further, since the prior art barrier has no peripheral flange, it does not protect the meeting plane of the barrier and the trapezoidal tabs, allowing the cavity under the brace to collect melting snow or acid rain which enters through a gap between the trapezoidal tabs and the down-roof surface of the barrier. When trapped liquid freezes in the cavity, expanding ice produces disruptive pressures on the seams of the brace. Moreover, trapped liquid accelerates what is referred to in the art as "internal weathering", and more correctly, corrosion. A more detailed comparison between the structural configuration of the prior art gusseted snow guard and the gusseted snow guard of this invention is provided herebelow in the Detailed Description.